Although a variety of methods have been developed, prediction of tachyarrhythmias and sudden cardiac death remains a difficult and often imperfect procedure. Recently, analysis of microvolt level T-wave alternans (TWA) has been introduced as a new approach to evaluate arrhythmia risk. TWA, an ECG phenomenon, is a manifestation of the intrinsic heart instabilities. The underling causes of tachyarrhythmia and sudden cardiac death are believed to be the alternans in electrical wave propagation and action potential repolarization.
The following articles, which are incorporated herein by reference, provide additional details about T-wave alternans analysis: Pastore et al. “Mechanism linking T-wave alternans to the genesis of cardiac fibrillation.” Circulation. 1999 Mar. 16; 99(10):1385-94; and Shimizu et al. “Cellular and ionic basis for T-wave alternans under long-QT conditions.” Circulation. 1999 Mar. 23; 99(11):1499-507.
The degree of T-wave alterations has been found to be tightly associated with heart diseases such as ischemia, myocardial infarction, heart failure, etc. However, it has generally been believed that a substantially elevated heart rate is required in order to detect TWA, which would be unpleasant and potentially arrhythmogenic procedure for certain patient populations. It would be beneficial if TWA, or more generally, electrical alternans, could be detected at normal heart rates.